Another explanation is that the more space between 2 galaxies, the more that space expands. Say you have 12 ft of rope. Every 5 minutes is expands by 1 in per foot. After the first cycle you have 13 ft of rope After the 2nd, 14ft 1in After the 3rd, 15ft ~3in The longer the rope, the faster it expands.

Wait, how do we know it's "several times" bigger than the observable? I haven't seen anything to reference the actual size of the entire universe beyond observable.

Going back to the balloon analogy, the dots are moving away from each other. Without the vertical dimension, the "universe" of the balloon surface is getting bigger, but what is it expanding into? The space between dots is expanding, but where is the space coming from?

In this model, the dots dont understand elastic stretching. In the universe, it's believed that empty space is just expanding and pushing everything apart, but we don't know how.